The energetic efficiency of the refrigeration compressors is mostly attributed to the good performance of their valves in the control of the gas flow.
In the reciprocating refrigeration compressors, the compression of the refrigerant gas is obtained by movement of the piston, which is driven by a driving means, such as a mechanism of the connecting rod-crankshaft type, or by a linear motor. The piston slides, in a reciprocating movement, in the interior of a compression chamber defined in the block of the compressor. At the moment in which the piston begins to return from the upper dead point to the lower dead point, in its suction stroke, it draws the refrigerant gas from the suction line of the refrigeration system to which the compressor is coupled (that is, it draws the refrigerant gas coming from the evaporator of the refrigeration system). Subsequently, when said piston returns from the lower dead point, in its compression stroke, it compresses the refrigerant gas which, under high pressure (of condensation), flows through the discharge system and returns to the refrigeration system to which the compressor is coupled.
Reciprocating refrigeration compressors use one way valves to control the gas flow during operation thereof. The valve systems provided in a valve plate, in the head region of the compressor, are responsible for regulating the flowrate and optimizing the dynamics of the gas flowing during the suction and the discharge of refrigerant gas in relation to the compression chamber.
A suction valve controls the gas flow coming from the suction line connected to the low pressure side of the refrigeration system and which is drawn into the interior of the compression chamber, whilst a discharge valve controls the already compressed gas flow to be directed to the high pressure side of the refrigeration system, said valves being designed to have their opening and closing pendular movement synchronized with the movement of the piston.
The suction and discharge valves are generally constituted of flexible vanes, which are fixed by one of the ends thereof and operatively associated with one or more passage orifices, so that, when the pressure differential is established through the valve, the flexible vane moves, by elastic deformation, away from the respective passage orifice, allowing the passage of the gas in the required preferential direction.
There are known countless embodiments of suction valves for reciprocating refrigeration compressors, regarding the project of the flexible vane (obturator element), of the valve seat, of the gas passage orifice and also the way the valve parts are attached.
Single-Piece Suction Valves
As illustrated in FIG. 1 of the enclosed drawings, the single-piece suction valves V, formed in a single piece, are generally obtained by stamping a high carbon or stainless steel sheet. This stamping operation allows the suction valve V to present, in a single piece, a flat spacer body 10 to be affixed between the crankcase 30 of the compressor and the valve plate 40, and a flexible vane 20, medianly disposed in relation to the spacer body 10 and having a fixing end portion 21 incorporated to the spacer body 10, and a bending median portion 22 and a sealing end portion 23, which are displaced in relation to the spacer body 10 during the opening of the suction valve V in relation to a respective passage orifice in the valve plate 40. As illustrated in FIG. 1, it is usually provided a sealing gasket 50 between the metal sheet of the suction valve V and the crankcase 30, said metal sheet generally presenting a contour corresponding to that of the valve plate 40.
After the step of stamping the metal sheet, the suction valve V is submitted to a tumbling operation, for rounding/finishing the edges of the flexible vane 20, so as to guarantee the latter to have a useful life compatible with that expected for the compressor.
In this type of construction, the spacer body 10 and the flexible vane 20 are formed with the same material, and the radial gap between the flexible vane 20 and the spacer body 10 becomes oversized in relation to the gap which is required for the angular displacement of the flexible vane 20, for allowing not only the use of an adequately resistant stamping tool, but also the tumbling operation for rounding the edges of said movable portions of the vane. The need of a radial gap between the flexible vane 20 and the spacer body 10 provokes an undesirable increase of the dead volume of the compressor, impairing its volumetric efficiency.
It is known that one of the alternatives for reducing the suction losses of the compressor is to reduce the stiffness of the flexible vanes, which can be obtained by reducing the metal sheet thickness, but maintaining the same geometry of the flexible vane 20. However, it is necessary that the flexible vanes 20 present high impact and bending strength, which can be obtained with the use of nobler materials, which must be applied not only to the flexible vane 20, but also to the spacer body 10, in a single-piece with the vane, undesirably increasing the cost of the single-piece suction valve V.
Vane-Type Suction Valves
In an alternative known prior art construction, as described and illustrated in Brazilian patent document PI0505734-5 (WO2007/070995), the single-piece suction valve is replaced by a valve comprising only the flexible vane to be secured to the valve plate. These vane-type suction valves allow a significant reduction of the production costs, making the peripheral finishing by tumbling easier and allowing the flexible vane, as a single piece, to be formed in nobler materials of higher cost.
Nevertheless, considering that the flexible vane must be mounted between the confronting face of the valve plate and the sealing gasket to be seated against the block of the compressor, a problem occurs in that the sealing gasket has to “absorb” the thickness of the flexible vane. It should be noted that, although being compressible in its thickness, the sealing gasket admits a degree of compression which is insufficient to absorb or compensate for the thickness of the flexible vane disposed between the compressor block and the confronting face of the valve plate.
In order to overcome the problem regarding the seating of the flexible vane against the confronting face of the valve plate, it is known to provide a recess in the compressor block or in the valve plate (see solution described in document WO2007/070995), with the object of avoiding the problem of its thickness being “absorbed” by the sealing gasket, and guaranteeing the desired degree of sealing for the compression chamber.
However, the process for manufacturing the recess in the compressor block or in the valve plate requires a precise tolerance control for the recess depth. If the depth of the recess is lower than the thickness of the flexible vane, and the sealing gasket is not capable to deform under compression, so as to absorb the “excess” of thickness of the flexible vane, the required sealing degree will not be reached, resulting in leaks in the compression chamber after mounting the parts of flexible vane, sealing gasket, valve plate and head to the compressor block. On the other hand, when the depth of the recess is higher than the thickness of the flexible vane and the sealing gasket is not capable of compensating for this difference, there will occur leak in the compression chamber after mounting the parts responsible for the closing thereof. Considering that the manufacturing thickness of the flexible vanes varies by about 0.005 mm, the processes for manufacturing the recess in the valve plate with this margin of tolerance tends to increase the cost of this solution.
As it occurs in the solution described in document WO2007/070995, the flexible vane can have its fixing end portion attached to the valve plate by means of pins, by welding or by being only correctly positioned before the final mounting of the head.
The recess, when located in the valve plate, can be obtained during the sintering process of the valve plate or it can be machined afterwards. Even when the recess is obtained during the sintering of the valve plate, it is desirable to provide a surface finishing operation for the annular region which defines the seat for the seating of the sealing end portion of the flexible vane, so as to avoid leaks upon closing the suction valve, as well as the existence of peaks on the surface, which situations can impair the reliability of the suction valve. This surface finishing operation requires some reference points to guarantee the annular seat is parallel to the remaining recess surface. Irregularities on the recess surface may impair the alignment between the fixing end portion of the flexible vane and the annular seat of the suction valve, which can generate leaks during operation of the compressor. Besides, the finishing operations of surfaces presenting recesses can substantially increase the production costs, as compared with operations for finishing smooth surfaces, and even annul the advantages related to the vane-type suction valves.
Two-Piece Suction Valves
FIGS. 2, 3 and 4 illustrate known constructions of two-piece suction valves comprising a spacer body 10, formed in a relatively low cost material, and a flexible vane 20, formed in a separate piece with a noble material, to comply with the operational requirements of the compressor.
This two-piece construction also allows stamping two different pieces and tumbling them separately, without excessively increasing the radial gap (dead volume) and allowing a better finishing for the edges of the two pieces.
Nevertheless, although not presenting the limitations of the single-piece suction valve construction, which has two component-parts formed in a single piece, this solution comprising two different pieces presents the disadvantage of requiring additional procedures and measures for joining the spacer body and flexible vane to each other, and then for mounting them to the valve plate, in order to guarantee the correct positioning of the flexible vane in the latter, before affixing the valve plate to the crankcase 30 (illustrated only in FIG. I).
The solution illustrated in FIG. 2 is described in Brazilian patent document PI9604645-7 and requires the use of a fixation element as, for example, an adhesive tape 60, to maintain the flexible vane 20 secured to the spacer body 10 in a predetermined position, before mounting the assembly formed by the two pieces of the valve, against the crankcase 30, with the interposition of the sealing gasket. This prior art solution requires the flexible vane 20 to be previously attached to the spacer body 10, before affixing the assembly to the compressor.
In case of using the adhesive tape 60 as a means for affixing the flexible vane 20 to the spacer body 10, this fixation element must present a reduced thickness and be inert to the working fluid of the compressor, so as not to deteriorate along the useful life of the latter, at the risk of obstructing the system, reducing the efficiency of the compressor or even stopping the operation thereof. In order to facilitate the stacking of the assembly formed by the flexible vane 20 and by the spacer body 10, a second adhesive tape can be used in a position diametrically opposite to the first one. Thus, these components previously affixed to each other require measures upon handling, shipping and storage, so that the flexible vane 20 does not detach from the spacer body 10. The solution illustrated in FIG. 3 is described in patent document U.S. Pat. No. 5,140,748 and also requires additional fixation elements for the two pieces of the valve, to attach the flexible vane 20 to the spacer body 10 and the assembly formed thereby to the valve plate 40. The fixation elements are defined by pins 70 which require, for their application, a drilling operation in both the valve plate and the compressor block. This solution has the inconvenience of presenting cost increments related to the production of pins and holes for the fitting in the compressor block and in the valve plate, as well as to the complexity of the manufacturing and mounting processes.
FIG. 4 refers to a construction described in patent document U.S. Pat. No. 6,227,825 and which also considers the previous fixation of the flexible vane 20 to the spacer body 10, before affixing the assembly formed by the two components of the valve to the compressor.
The fixation of the two pieces of the suction valve to each other is carried out by a fixation means, such as adhesive, welding, brazing, laser and the like, which need some care. If the joining of the two materials is made by means of an adhesive material, the measures taken for handling and shipping should be such as to avoid the flexible vane 20 and the spacer body 10 from separating from each other. The properties of the flexible vane cannot suffer physical or chemical alterations, after the joining process, at the risk of compromising its useful life. Since the materials generally have different mechanical properties and different chemical compositions, it is necessary to choose a joining process, by means of welding, brazing, etc., which preserves the characteristics of the material, especially the material of the vane. Also during the joining process, it cannot occur excessive deposition of material which surpasses the nominal thickness of the metal sheets which define the two valve pieces, which can cause leaks in the compression chamber, with harmful impact on the efficiency of the compressor.
The butt joint, between the fixing end portion of the vane and the spacer body, is a process which requires additional measures, mainly due to the reduced thickness of the metal sheets from which the flexible vane and the spacer body are manufactured.
In short, the process for affixing the vane and the spacer body to each other requires several cares, and may compromise the reduction of cost obtained by using a less noble material in the spacer body.